Electronic devices such as power amplifiers, power supplies, multi-chip modules, electronic hybrid assemblies such as power amplifiers, microprocessors and passive components such as filters may contain heat sources which require cooling during normal operation. Various techniques may be used for cooling electronic devices. Traditionally, electronic devices have been cooled by natural or forced air convection which involves moving air past conduction heat sinks attached directly or indirectly to the devices.
Efforts to reduce the size of devices have focused upon increased integration of electronic components. Sophisticated thermal management techniques using liquids, which allow further abatement of device sizes, have often been employed to dissipate the heat generated by integrated electronics.
Two-phase thermosyphons have been developed to provide cooling for electronic devices. Two-phase thermosyphons typically include a two-phase material within a housing. The two-phase material, typically a liquid, vaporizes when sufficient heat density is applied to the liquid in the evaporator section. The vapor generated in the evaporator section moves away from the liquid towards the condenser. In the condenser section, the vapor transforms back to liquid by rejecting heat to the ambient. This phase-change cycle is used to spread the heat dissipated by discrete devices over a larger area, resulting in lower device temperatures compared to conventional heat sinks.
The heat transferred by a two-phase thermosyphon can be dissipated to the ambient by a variety of means, e.g., natural air convection, forced air convection, liquid convection, etc. A natural air convection cooled two-phase thermosyphon consists of heat rejecting fins on the exterior surface of the condenser section. In many cases, it is desirable to mount the two-phase thermosyphon, which forms the main heat sink of an electronic assembly, in different orientations with respect to gravity. However, both the internal and external heat transfer processes in a natural convection cooled two-phase thermosyphon depend primarily on gravity. As a result, varying the orientation with respect to gravity usually leads to large degradations in thermal performance.
There is therefore a need for a natural convection cooled two-phase thermosyphon, which yields good thermal performance over a range of orientations with respect to gravity.